The field of the invention deals with a double scanning, preferably stereo-radiographic, system and a method to optimize the radiation, preferably x-ray, scattering rejection and correction in order to acquire at least two simultaneous views, preferably frontal and lateral view images for low dose three dimensional reconstruction of an organ, preferably the skeleton, of patients for medical applications.
This system and method are dedicated to be used within medical radiology devices including at least two radiation, preferably x-ray, transmissions based imaging capabilities. These capabilities will be based on for example at least an x-ray emission source emitting x-ray spectra having a higher energy comprised between 20 keV and 200 keV. The typical imaged object is a patient in weight bearing position.
A scanning stereo-radiographic system such as the one described in EP 2309462 demonstrated good capabilities to make simultaneous frontal and lateral images for three dimensional reconstruction of skeletal anatomical parts such as the rachis or pelvis with a dose reduction up to 600 compared to Computed Tomography scan, and also a dose reduction up to 10 for single view images compared to Computed Radiography or Digital Radiography systems. But the maximum available dose rate of this system has also become a growing limitation to produce enough clinical quality images of overweight and obese patients, all the more that overweight and obese patients are nowadays very common patients.
One important problem to make some good clinical quality radiology images on overweight and obese patients is the big amount of scattered x-rays created while the direct x-ray beam is much attenuated. Thus, the transmitted direct x-ray signal can become very small, typically 10-20 times lower, in comparison with the scattered x-ray signal in direct two dimensional imaging systems.
Some scattering rejection grids are commonly used to solve this problem, but taken alone, their efficiency is not good enough, and therefore the dose on overweight and obese patients can become very high in order to get clinical quality images.
A scanning stereo-radiographic system such as the one described in EP 2309462 demonstrates an efficient scattered x-ray rejection using a very thin object and detector collimations. But the useful dose rate fraction to make the image becomes too small for overweight patients. Some of the reasons are the limited output power of x-ray tubes and the very small collimation apertures.
According to such a prior art, for example described in EP 2309462, there is described a radiology method performing vertical scanning. This radiology method used collimators located upstream detectors, thereby improving cross-scattering and self-scattering rejection. However, high rejection rate was achieved thanks to narrow collimation thereby at the expense of lowering much the level of received radiation signal on the sensitive surfaces of the detectors. Therefore, at least for some patient organs, when used with reasonably overweight patients, it was difficult, and when used with really overweight or even obese patients, it was not possible, to find a good compromise between a high rate of scattering rejection and simultaneously a sufficient level of received radiation signal on the sensitive surfaces of the detectors.
A system to tune the aperture of the collimation according to the patient morphology such as the one described in another prior art, for example described in WO 2011/138632, could be used to enhance the ability to make clinical quality images on overweight patients of the scanning stereo-radiographic system described in EP 2309462.
But, in this case, the output power of the x-ray tube and available collimation aperture of the detector would not be enough to cover the whole growing population of the varied morphologies among overweight and obese patients. The aperture limitation will be directly linked with the loss of spatial resolution of the detector and the amount of scattered x-ray coming from both x-ray imaging frontal and lateral views. The use of coplanar simultaneous frontal and lateral x-ray views will create a specific problem of cross-scattering in addition to the self-scattering pollution of each view.